Platform positioning system

Abstract

A system for precisely positioning and moving a platform, with at least four and preferably six degrees of freedom, relative to a frame is disclosed herein. The platform is particularly suitable for carrying wafers. Charged particle optics can be attached to the frame, in which case any point on the wafer can be positioned to within at least one micron relative to the charged particle optics. The charged particle optics may comprise multiple columns, each column generating at least one charged particle beam. The platform positioning system comprises a base; a frame attached to the base; a stage, comprising a platform and stage actuators, coupled to the base and the frame; stage sensors, for sensing the position of the stage relative to the frame, rigidly coupled to the frame; and a current control system coupled to the stage sensors and the stage actuators. The current control system in its simplest form comprises a trajectory generator, a conversion matrix, a feedforward controller, a feedback controller, an adder and steering matrix, and a current amplifier.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001] This application is a continuation of US application Nos. 09 / 543,265 and 09 / 543,283, both filed on Apr. 5, 2000, both of which claim the benefit of U.S. Provisional Application No. 60 / 163,846 filed Nov. 5, 1999.BACKGROUND OF THE INVENTION[0002] 1. Field of the Invention[0003] This invention relates to the field of control systems for precision stages, and in particular to control systems for stages for use in multi-column charged particle lithography, test and inspection systems.[0004] 2. Description of the Related Art[0005] Precision stages find many applications with steadily increasing precision requirements. In semiconductor capital equipment, for example, precision stages are required for carrying wafers during lithography process steps. As the length scales of microcircuit features become smaller, modem lithography moves toward the use of higher resolution techniques, for example phase shift masks, extreme ultraviolet (EUV) systems...

AI Technical Summary

Benefits of technology

[0014] For use in applications such as charged particle lithography, charged particle optics can be attached to certain embodiments of the frame of the platform positioning system, resulting in a charged particle beam system. The charged particle optics can comprise multiple columns, each column generating at least one charged particle beam. In certain embodiments the charged particle optics can generate electron beams. In certain embodiments of the invention the current control system includes a predictor which sends signals to a deflection system, included in the charged particle optics, allowing more accurate placement of charged particle beams on a moving platform. The platform can comprise a wafer chuck. In preferred embodiments, any point on a wafer, placed on the wafer chuck, can be positioned relative to the charged particle optics with an accuracy of at least one micrometer.

Problems solved by technology

However, in charged particle beam lithography systems, vacuum and high voltage compatibility is an inherent design complication.

However, in a system where up to 100 kV potential difference must be held off with no arcing or other undesirable effects, close mechanical coupling of non-insulating components, such as illustrated in FIG. 1, would be inappropriate.

In regard to vacuum compatibility, many prior art stages are inappropriate for use in a high vacuum due to bearing designs that are prone to out-gassing, generating particulates, or otherwise contaminating the vacuum system.

However, most prior art flexural bearings are potentially unstable when used as thrust bearings since the flexural joint is prone to distortion or buckling under compressive loads.

Further, for positioning systems requiring precision movement and short times to reach a steady-state position (settling times) after each movement, attention must be paid to perturbations that are insignificant for less precise systems.

However, while a high inertia system tends to be mechanically stable, the reaction forces associated with moving a massive stage can degrade the accuracy and precision of the relative positioning of the lithography optics and the work platform, unless a long settling time is accepted.

The resulting weight and volume of such devices is undesirable.

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